Many voice and data communication devices particularly those used in mobile applications, operate using multiple units. One of these units is generally used for operator interface. Functions controlled by these units are channel selection, volume control, microphone and speaker connections, etc. A second unit, remotely located, is used to handle the transmission and reception of radio frequency signals. The connection between the two units has traditionally been provided by multi-wire cables. These cables are generally complex and have many different types of inner wires for handling various signal types namely; audio and digital signals. Additionally, these cables are expensive and unreliable.
In the past many attempts have been made to reduce the number of wires used in these cables. One such reduction has been the use of a limited number of wires to handle all the commands entered by the operator by serially placing those commands of these wires. In U.S. Pat. No. 4,147,984 to Caudel et al. discloses a dual digital processor radio signal transmitter having two units coupled to each other via a pair of wires. The communication device in his claims communicates the selection of a key from one unit to another digitally and serially. The voice communication is either not provided for or is carried by a second pair of wires. Other methods are available for communications between register-modeled radio devices using data packets with reduced number of wires (U.S. Pat. Nos. 4,637,022 and 4,684,941). Neither of these methods provide for voice communications. It is therefore clear that a need exists for a communication device having multi-units coupled to each other via a single pair of wires and being able to simultaneously process voice and digital information between its multi-units.